Doxycycline vs Azithromycin for Chlamydia: Which One Should You Take?

If you have just been prescribed an antibiotic for chlamydia, you may have received one of two: doxycycline (a 7-day course) or azithromycin (a single dose). Both work against Chlamydia trachomatis. But in 2021, the CDC quietly updated its treatment guidelines to make doxycycline the first-line choice for nearly all chlamydia infections, with azithromycin reserved for specific scenarios.

Here is what changed, why it changed, and what it means for you.

The short answer

For most adults with uncomplicated genital chlamydia, the current CDC-recommended treatment is:

  • Doxycycline 100 mg orally, twice daily, for 7 days

Azithromycin (1 gram single dose) is now an alternative rather than first-line, used in scenarios like:

  • Pregnancy (where doxycycline is contraindicated)
  • Confirmed or strongly suspected non-adherence to a 7-day course
  • Expedited partner therapy when a follow-up cannot be guaranteed

The change reflects updated evidence on bacterial cure rates and resistance trends.

Why CDC moved away from single-dose azithromycin

For years, the standard first-line treatment for chlamydia in the United States was a single oral 1-gram dose of azithromycin. It was popular for an obvious reason: one pill, in the clinic, observed by the provider — no adherence question. Patient compliance was guaranteed in a way doxycycline never was.

But over the 2010s, several large studies began showing higher microbiological failure rates for azithromycin, especially for rectal chlamydia infections. Some studies found cure rates as low as 70-80% for rectal disease with single-dose azithromycin, compared with 95%+ for the 7-day doxycycline course.

The 2021 CDC STI Treatment Guidelines reviewed this evidence and changed the recommendation. For all anatomic sites of chlamydia in non-pregnant adults, doxycycline is now first-line.

When azithromycin is still preferred

Azithromycin has not disappeared from the treatment guidelines — it remains the right choice in a handful of clinical scenarios:

Pregnancy

Doxycycline is in the tetracycline class, which is contraindicated in pregnancy after the first trimester because it can affect fetal bone and tooth development. For pregnant patients with chlamydia, azithromycin 1 g single dose orally is the recommended treatment.

Strong concern about adherence

If a clinician believes a patient will not complete a 7-day course (for instance, an unhoused patient, a patient with significant mental-health concerns, or someone presenting for episodic care), single-dose azithromycin observed in the clinic is reasonable.

Expedited partner therapy

Expedited partner therapy (EPT) is when a clinician sends antibiotics home with the diagnosed patient for their partner(s) — without seeing the partner first. Because there is no way to confirm the partner will complete a 7-day course unobserved, single-dose azithromycin is preferred for EPT in most U.S. jurisdictions.

Doxycycline vs azithromycin — side effects compared

Both medications are well tolerated by most people. The side-effect profiles differ:

Doxycycline common side effects:

  • Photosensitivity (sun-sensitivity rash) — use sunscreen and avoid prolonged sun
  • Esophagitis if taken without enough water
  • Nausea (take with food)
  • Yeast infections
  • Rare: pseudotumor cerebri

Azithromycin common side effects:

  • GI upset — diarrhea, nausea, vomiting (more common with the 1-g dose)
  • QT prolongation (relevant in patients with cardiac risk factors)
  • Allergic reactions

For most healthy adults, the choice between them is driven by clinical factors (pregnancy, adherence, infection site) rather than tolerability.

How to take doxycycline correctly

Doxycycline works only if you complete the full 7-day course. To get the best outcome:

  1. Take with a full glass of water, sitting upright, at least 30 minutes before lying down. This prevents the pill from causing esophagitis.
  2. Take with food — it reduces nausea without significantly reducing absorption (unlike older tetracyclines).
  3. Do not skip doses. Twice-daily means roughly every 12 hours. Pick mealtimes that anchor it (breakfast and dinner work for most people).
  4. Avoid antacids, calcium supplements, iron, dairy heavy meals, and bismuth (Pepto-Bismol) within 2 hours of the dose. They bind doxycycline and block absorption.
  5. Use sunscreen and avoid extended sun exposure — doxycycline causes photosensitivity in many users.
  6. No alcohol restriction is required, but heavy drinking interferes with adherence and is best avoided.
  7. Avoid sex until at least 7 days after the last dose — and only after your partner has been treated.

Test-of-cure: do I need to test again after treatment?

Routine test-of-cure (re-testing immediately after treatment to confirm the infection is gone) is NOT recommended for uncomplicated genital chlamydia in non-pregnant adults treated with doxycycline. The reason: doxycycline cure rates are high enough that routine retesting is not cost-effective.

What IS recommended:

  • Retest at 3 months after treatment. This is not a test-of-cure — it is a test for reinfection, which is common because partners may not have been treated. Roughly 15-20% of treated patients are reinfected within 6 months.
  • Test-of-cure is recommended for pregnant patients, anyone treated with a non-first-line regimen, anyone with persistent symptoms, and anyone whose treatment adherence is uncertain.

What if you have already taken azithromycin?

If you were prescribed azithromycin 1 g for chlamydia before the 2021 update — or if your clinician chose azithromycin for a reason — you are not in trouble. Single-dose azithromycin still works for the majority of genital chlamydia. But:

  • If your symptoms persist beyond 1-2 weeks, retest rather than assume it failed.
  • If you had rectal chlamydia, talk to your clinician about whether a follow-up test makes sense, since rectal cure rates with azithromycin are lower.

The bottom line

For most adults newly diagnosed with chlamydia in 2026:

  • First choice: doxycycline 100 mg twice daily for 7 days
  • Pregnancy: azithromycin 1 g single dose
  • Partner therapy / adherence concerns: azithromycin 1 g single dose

Both medications cure most chlamydia infections. The shift to doxycycline as first-line reflects modestly better bacterial cure rates — especially for rectal infections — not a problem with azithromycin.

Take the full course. Wait 7 days before sex. Make sure partners are treated. Get retested at 3 months. That is the playbook.

For more on chlamydia — symptoms, testing, oral chlamydia, fertility risks, and what to expect after treatment — see our complete chlamydia pillar guide. If you are walking through a diagnosis and want anonymous community support, join Shameless Path.

Sources:

  • CDC. Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR 2021;70(4).
  • Kong et al. Azithromycin versus doxycycline for the treatment of genital chlamydia infection. Clin Infect Dis 2014.
  • Páez-Canro et al. Antibiotics for treating urogenital Chlamydia trachomatis infection in men and non-pregnant women. Cochrane Review 2019.